I have both Mozilla and Internet Explorer installed on my machine. I use them both for browsing. I’d like to make Mozilla completely unable to use Macromedia Flash while leaving that functionality unaffected in IE. I’ve gone through the entire Mozilla directory and deleted every file that looks like it had something to do with Flash, but Flash animations still play in Mozilla. I can’t find anything in the Mozilla preferences which says which plug-ins to use.
Flashblock looks like it will do what you want. I haven’t used this, though, so I don’t know how well it works.
There are also Mozilla extensions which give you buttons to kill Flash on a per-page basis. One of them is PrefBar, which is useful for lots of other things too.
Also, if you have WinXP SP2, you can disable any plugins on the fly. Through Tools->Options and in the Programs page, select Manage Add-ons. You can turn off Flash and then turn it back on any time. It’s a pretty nifty feature :).